1. Field of the Invention
This invention relates in general to in situ formation of magnetic media subsequent to coating, and in particular to formation in situ of discrete magnetic particles from a coating including nickel and hypophosphite functioning as sensitizing agents, by exposure to radiant energy, and particularly x-rays and electron beam radiation sufficient to form nickel nuclei in the coating, and developing the exposed areas with a reducing agent, such as sodium hypophosphite, in solution with cobalt, nickel and/or iron ions.
2. Description of the Related Art
Electroless deposition of metals under reducing conditions has been known for various purposes. The resulting coating may be in the form of a continuous metal layer, i.e. plating, or may be deposited image-wise by, for instance, exposure to x-ray radiation in a photographic process.
U.S. Pat. No. 3,762,938 discloses a reducing process for depositing metal coatings on substrates. U.S. Pat. Nos. 3,378,410 and 3,658,569 disclose methods for image-wise production of metallic coatings utilizing an electron beam as a photographic or graphics art production method. Similarly, U.S. Pat. No. 3,920,485 discloses the use of an electron beam to form platelets of a metallic substance for utilization in thin film technology to produce electronic circuitry devices.
U.S. Pat. Nos. 3,607,218, 3,726,664 and 4,059,463 disclose procedures for producing fine magnetic particles by reducing from solution magnetic metal salts by, for instance, exposure to hypophosphite ions. However, the purpose of these patents is the production of the particles per se, which are thereafter conventionally milled with binders to produce coatings to form magnetic media, such as tapes and disks.
Thus, in summary, the related art is concerned with reduction of metallic salts to form reduced metal plating and images without significant magnetic properties, or, alternatively, to form particles adapted to be included in an admixture with a binder for production of discrete magnetic particles in a layer. The latter process, which is often accomplished by extensive ball milling of the magnetic particles with a binder, results in degradation and breaking of the magnetic particles through forceful physical processes such as ball milling, extrusion coating, calendering, etc.